1. Field of the Invention
The present invention relates to an audio signal processing device which carries out various types of processing on audio signal, and in particular to an audio signal processing device which processes monaural signals input thereto.
The present application claims priority on Japanese Patent Application No. 2011-235211, the entire content of which is incorporated herein by reference.
2. Description of the Related Art
Audio signal processing devices for processing audio signals such as monaural signals have been conventionally known. For example, Patent Literature 1 discloses a surround reproduction circuit which produces a monaural surround signal widely propagating sound into the surrounding space with a monaural speaker. Specifically, the surround reproduction circuit receives a right-channel signal (R) and a left-channel signal (L) so as to produce a difference signal L−R and a composite signal L+R. The difference signal L−R is supplied to a low-pass filter, multiplied with a predetermined gain, and then added to the composite signal L+R, thus achieving a widely propagating effect of sound.
The surround reproduction circuit of Patent Literature 1 includes a low-pass filter, which in turn causes an acoustic deficiency in which the high-frequency range of a difference signal L−R may undergo phase variation while the low-frequency range may not undergo phase variation. Thus, frequency characteristics will be disintegrated when the difference signal L−R is added to the composite signal L+R. Additionally, a higher gain applied to the difference signal L−R may excessively enhance the low-frequency range of sound.